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# Binomial With Extra Term watch

1. So I'm self teaching the linear maths course and going through the textbook question, it has a bad habit of giving questions that haven't been explained at all -> example:
Find the coefficient of x^4 in the expansion of (1+x)(2x-3)^5
There must be a shorter way of solving this than fully expanding the binomial then multiplying it by the extra terms?
2. (Original post by AmmarTa)
So I'm self teaching the linear maths course and going through the textbook question, it has a bad habit of giving questions that haven't been explained at all -> example:
Find the coefficient of x^4 in the expansion of (1+x)(2x-3)^5
There must be a shorter way of solving this than fully expanding the binomial then multiplying it by the extra terms?
Yes there is, and you get it through practice.

That there is the same as and essentially you're interested in so replace the by the term with from the expansion, and replace with the term of the expansion, then simplify the second term, add the two together to get it.
3. (Original post by RDKGames)
Yes there is, and you get it through practice.

That there is the same as and essentially you're interested in so replace the by the term with from the expansion, and replace with the term of the expansion, then simplify the second term, add the two together to get it.
Oh yeah! That's actually quite obvious in retrospect, thank you very much!

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